IPlatformSettings.PreferredApplicationLanguage API

[maxkatz6]

What does the pull request do?

public interface IPlatformSettings
{
+        /// <summary>
+        /// Gets the preferred application language as specified in the operating system settings.
+        /// </summary>
+        string PreferredApplicationLanguage { get; }

+        /// <summary>
+        /// Raises when the preferred application language is changed in the operating system settings.
+        /// </summary>
+        event EventHandler? PreferredApplicationLanguageChanged;
}

Status

• Default - fallbacks to CultureInfo.CurrentUICulture.Name, not sure if it's ideal
• Windows - GetUserDefaultLocaleName
• Browser - navigator.language
• macOS
• Linux (is LANG/LC_MESSAGES env variable is the only option really? there is a GTK specific API though...)
• iOS
• Android

Checklist

• Added unit tests (if possible)?
• Added XML documentation to any related classes?
• Consider submitting a PR to https://github.com/AvaloniaUI/avalonia-docs with user documentation

Fixed issues

Partially implements #19402